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rcu: Ensure that ->rcu_urgent_qs is set before resched IPI

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The RCU-specific resched_cpu() function sends a resched IPI to the
specified CPU, which can be used to force the tick on for a given
nohz_full CPU.  This is needed when this nohz_full CPU is looping in the
kernel while blocking the current grace period.  However, for the tick
to actually be forced on in all cases, that CPU's rcu_data structure's
->rcu_urgent_qs flag must be set beforehand.  This commit therefore
causes rcu_implicit_dynticks_qs() to set this flag prior to invoking
resched_cpu() on a holdout nohz_full CPU.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Joel Fernandes (Google) 2019-08-15 22:59:14 -04:00 committed by Paul E. McKenney
parent 5a6446626d
commit 05ef9e9eb3
1 changed files with 1 additions and 0 deletions
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kernel/rcu/tree.c
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@ -1073,6 +1073,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
if (tick_nohz_full_cpu(rdp->cpu) &&
time_after(jiffies,
READ_ONCE(rdp->last_fqs_resched) + jtsq * 3)) {
WRITE_ONCE(*ruqp, true);
resched_cpu(rdp->cpu);
WRITE_ONCE(rdp->last_fqs_resched, jiffies);
}